Many types of microchips, such as MEMS accelerometers, can malfunction if exposed to the environment. For example, if exposed to the environment, moisture and debris may settle between a suspended mass and substrate of a conventional accelerometer. As a result, the mass may stick to the substrate, thus causing the accelerometer to provide no output signal indicative of actual acceleration. This can present a very dangerous situation when used as part of a safety device, such as an automobile airbag system.
The art responded to this problem by often hermetically sealing environmentally sensitive components within a microchip package. For example, an accelerometer die may have either a cap over the sensitive microstructure (effectively forming a wafer level package), or a separate package completely containing the entire die. In either case, the package hermetically seals the sensitive microstructure within the package interior, protecting it from the environment.
During use, however, some packages undesirably may lose their hermeticity.